1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an inkjet printing method employed for printing images by ejecting ink onto a print medium.
2. Description of the Related Art
At present, printing apparatuses that eject ink droplets from a print head to perform printing has been widely employed as output apparatuses. In a printing apparatus that employs this system, there is a printing apparatus that ejects ink droplets from ejection ports that are formed in a print head, and forms dots on a print medium to print an image. For substantially filling a specific predetermined area of a print medium with a single color, ink dots are formed in that area by ejecting ink droplets at a high dot print density. However, in a case wherein too many ink droplets are ejected into the print area of predetermined size, ink bleeding occurs both inside and outside the print area, so that a clean outline of a printed image can not be obtained.
To resolve this problem, in Japanese Patent Laid-Open No. 2002-113850 an ink jet printing apparatus is disclosed for which a print area is divided into an outer area and an inner area, and the ink employed for printing each of the printing areas differs, depending on which area is to be printed. According to the printing apparatus disclosed in Japanese Patent Laid-Open No. 2002-113850, for the outer area, ink having a relatively low permeation rate (ink that relatively slowly permeates a print medium; hereinafter referred to as low-permeation ink) is employed to form dots, while for the inner area, ink having a relatively high permeation rate (ink that relatively rapidly permeates a print medium; hereinafter referred to as high-permeation ink) and the low-permeation ink are employed for form dots. Since the two types of ink, which have different permeation rates, are employed for printing the inner area, the period required for a print medium to dry can be reduced, compared with when only low-permeation ink having a low permeation rate is employed for printing, and as a result, the printing speed can be increased. Furthermore, compared with when only high-permeation ink is employed for printing the inner area, ink bleed can be reduced, and degradation of the quality of a printed image can be avoided.
When the printing apparatus disclosed in Japanese Patent Laid-Open No. 2002-113850 is used for printing, two types of ink dots having different permeation rates are alternately formed, in a staggered pattern, into the inner area. That is, in the inner area, dots of high-permeation ink and dots of low-permeation ink coexist. However, in Japanese Patent Laid-Open No. 2002-113850, it states simply that dots of the two types of ink, which have different permeation rates, are alternately formed in the inner area of an image being printed by the printing apparatus, and the order in which these two types of ink are ejected to form dots on a print medium is not specified. Therefore, it may logically be inferred that low-permeation ink droplets will be ejected into the print area after high-permeation ink droplets have been ejected. In such a case, the color component, such as a dye or a pigment, of the high-permeation ink deposited on the print medium may be drawn deep into the print medium, and the density of a dot could thereby be decreased. Therefore, the density of a part of a printed image may be insufficient, and the quality of the printed image degraded. This problem occurs when a dye is employed as the color material for an ink, but occurs more frequently when a pigment is employed as the color material.